Tilt sensor

A tilt sensor includes a mount board, a cover, a light emitting and two light receiving elements on the mount board. A case, provided between the mount board and the cover, is formed with an inner space surrounded by the light emitting element and the light receiving elements. A rolling member, movable in the inner space, can take a complete shielding position, a partial shielding position and an unshielding position. At the complete shielding position, the rolling member blocks the light from the light emitting element so that no light reaches the two light receiving elements. At the partial shielding position, the rolling member blocks the light so that the light reaches only one of the two light receiving elements. At the unshielding position, the rolling member does not block the light at all so that the light reaches the two light receiving elements.